Image sensors including photoelectric converting units having multiple impurity regions

ABSTRACT

An image sensor includes a semiconductor layer, and first and second photoelectric converting units including first and second impurity regions in the semiconductor layer that are spaced apart from each other and that are at about an equal depth in the semiconductor layer, each of the impurity regions including an upper region and a lower region. A width of the lower region of the first impurity region may be larger than a width of the lower region of the second impurity region, and widths of upper regions of the first and second impurity regions are equal.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from Korean Patent Application No.10-2007-0093286 filed on Sep. 13, 2007, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein byreference in its entirety.

BACKGROUND

The present invention relates to image sensors and methods ofmanufacturing the same, and, more particularly, to image sensors thatinclude photo-electric converting units for detecting differentwavelengths of light.

An image sensor converts an optical image into an electrical signal. Inrecent years, with the development of the computer industry and thecommunication industry, an image sensor that has an improved functionhas been increasingly demanded for various devices, such as digitalcameras, camcorders, PCSs (Personal Communication Systems), gamedevices, CCTV cameras, medical micro-cameras, and robots.

Some image sensors include color filters to reproduce colors of opticalimages. In image sensors that include color filters, when Bayer colorfilters are used, four unit pixels form one pixel group. In this case,the four unit pixels include two unit pixels that correspond to green,and two unit pixels that correspond to red and blue, respectively. Thatis, neighboring unit pixels are divided into red, green, and blue unitpixels that accumulate charges corresponding to the amount of incidentlight having wavelengths in the red, green, and blue regions,respectively. Each unit pixel includes a photoelectric-converting unitthat accumulates charges corresponding to the amount of incident light.

When the wavelength of incident light is long, the incident light willpenetrate more deeply into the semiconductor substrate. The wavelengthof red light is longer than the wavelength of green light, which is inturn longer than the wavelength of blue light. Accordingly, in the redunit pixel, the incident light penetrates more deeply into thesemiconductor substrate, but in the blue unit pixel, the incident lightdoes not penetrate as deeply into the semiconductor substrate. For thisreason, photoelectric-converting units that are provided in all of theunit pixels are formed deeply to collect all of the incident light.However, when impurities that form the photoelectric-converting unitsare implanted deeply into the semiconductor substrate, it is likely thatthe impurities will diffuse into adjacent regions. Accordingly, if thephotoelectric-converting units are formed to be deep, lower regions ofneighboring photoelectric-converting units may be easily connected dueto diffusion, and, thus, a phenomenon known as “blooming” may moreeasily occur.

Alternatively, in order to collect incident light of differentwavelengths, the photoelectric-converting units of the unit pixels canbe formed to have different depths according to the wavelength of lightdetected by the pixel. However, in order to form thephotoelectric-converting units of all the unit pixels to have differentdepths, it may be necessary to perform a photomask process at leastthree times, which can result in lower productivity and/or increaseddevelopment/manufacturing costs.

SUMMARY

An image sensor according to some embodiments includes a semiconductorlayer and first and second photoelectric converting units includingfirst and second impurity regions in the semiconductor layer that arespaced apart from each other and that are at about an equal depth in thesemiconductor layer, each of the impurity regions including an upperregion and a lower region. A width of the lower region of the firstimpurity region may be larger than a width of the lower region of thesecond impurity region, and widths of upper regions of the first andsecond impurity regions may be about equal. The semiconductor layer mayinclude a semiconductor substrate.

The image sensor may further include a third photoelectric convertingunit including a third impurity region in the semiconductor layer thatmay be spaced apart from the first and second impurity regions in thesemiconductor layer. A width of the third impurity region may be aboutequal to the widths of the upper regions of the first and secondimpurity regions, and a depth of the third impurity region may beshallower than depths of the first and second impurity regions.

The first impurity region may be configured to accumulate chargescorresponding to incident light having a wavelength in the red region,the second impurity region may be configured to accumulate chargescorresponding to incident light having a wavelength in the green region,and the third impurity region may be configured to accumulate chargescorresponding to incident light having a wavelength in the blue region.

The impurity concentration of the upper region of the first impurityregion may be higher than the impurity concentration of the lower regionof the first impurity region. The impurity concentration of the upperregion of the second impurity region may be higher than the impurityconcentration of the lower region of the second impurity region. Theimpurity concentration may be about equal in the lower regions of thefirst and second impurity regions.

The spacing between the upper regions of the first and second impurityregions may be smaller than the spacing between the lower regions of thefirst and second impurity regions. The width of the lower region of thesecond impurity region may be smaller than the width of the upper regionof the second impurity region. The first impurity region and the secondimpurity region may include impurity regions of the same conductivitytype.

An image sensor according to some embodiments includes a semiconductorlayer, and a plurality of unit pixels including red unit pixels, greenunit pixels, and blue unit pixels in the semiconductor layer. The red,green, and blue unit pixels may be configured to accumulate chargescorresponding to incident light having wavelengths in the red, green,and blue regions, respectively. Each of the plurality of unit pixels mayinclude a first impurity region of a first conductivity type that may beconfigured to accumulate charges corresponding to incident light of arespective wavelength. The red unit pixels include second impurityregions of the first conductivity type below the first impurity regions,and the green unit pixels include third impurity regions of the firstconductivity type below the first impurity regions and at about an equaldepth as the second impurity regions. The width of the third impurityregions may be smaller than the width of the second impurity regions.

The impurity concentration of the first impurity regions may be higherthan the impurity concentration of the second impurity regions and theimpurity concentration of the third impurity regions. The impurityconcentration of the second impurity regions and the third impurityregions may be about equal.

The first impurity regions may be spaced apart from each other, and aspacing between adjacent ones of the first impurity regions may besmaller than a spacing between adjacent ones of the second impurityregions and the third impurity regions. The width of the third impurityregions may be smaller than a width of the first impurity regions.

Methods of forming an image sensor according to some embodiments includedefining red unit pixel regions, green unit pixel regions, and blue unitpixel regions in a semiconductor layer, and forming a mask pattern onthe semiconductor layer. The mask pattern includes first openings overthe red unit pixel regions and second openings over the green unit pixelregions. The openings over the green unit pixel regions are smaller thanthe openings over the red unit pixel regions. The methods furtherinclude implanting ions into the semiconductor layer using the maskpattern as an ion implantation mask to form first impurity regions of afirst conductivity type in portions of the semiconductor layercorresponding to the red unit pixel regions, and to form second impurityregions of the first conductivity type in portions of the semiconductorlayer corresponding to the green unit pixel regions. The second impurityregions have a width smaller than a width of the first impurity regions.

Forming the mask pattern may include performing a photolithographyprocess using an optical mask including first light-transmittingportions in regions corresponding to the red unit pixel regions andsecond light-transmitting portions having a smaller area than the firstlight-transmitting portions in regions corresponding to the green unitpixel regions.

The methods may further include, after forming the first impurityregions and the second impurity regions, forming third impurity regionsof the first conductivity type in portions of the semiconductor layercorresponding to the respective regions. The third impurity regions maybe located above the first impurity regions and the second impurityregions.

The methods may further include, before forming the first impurityregions and the second impurity regions, forming third impurity regionsof the first conductivity type in portions of the semiconductor layercorresponding to the respective regions. The third impurity regions maybe located above the first impurity regions and the second impurityregions.

The impurity concentrations of the first impurity regions and the secondimpurity regions may be lower than an impurity concentration of thethird impurity regions. The depths of the first impurity regions and thesecond impurity regions may be about equal.

Methods of forming an image sensor according to some embodiments includeproviding a semiconductor layer, and forming first and secondphotoelectric converting units including impurity regions in thesemiconductor layer spaced apart from each other and at about an equaldepth, such that a width of a lower region of the first impurity regionis larger than a width of a lower region of the second impurity region,and widths of upper regions of the first and second impurity regions areabout equal.

The methods may further include forming a third impurity region spacedapart from the first and second impurity regions in the semiconductorlayer. The third impurity region may be formed to have about equal widthas the upper regions of the first and second impurity regions and adepth less than depths of the first and second impurity regions.

The impurity concentrations of the upper regions of the first and secondimpurity regions may be higher than impurity concentrations of the lowerregions of the first and second impurity regions.

The impurity concentration of the lower region of the first impurityregion may be about equal to the impurity concentration of the lowerregion of the second impurity region.

The spacing between the upper regions of the first and second impurityregions may be smaller than the spacing between the lower regions of thefirst and second impurity regions.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate certain embodiment(s) of theinvention. In the drawings:

FIG. 1 is a block diagram illustrating an image sensor according to someembodiments;

FIG. 2 is a circuit diagram illustrating a unit pixel of an image sensoraccording to some embodiments;

FIG. 3A is a layout diagram illustrating color filters of an imagesensor according to some embodiments;

FIG. 3B is a schematic plan view illustrating an active pixel sensorarray of an image sensor according to some embodiments;

FIG. 4 is a cross-sectional view taken along the line I-I′ of FIGS. 3Aand 3B;

FIG. 5A is a cross-sectional view taken along the line II-II′ FIGS. 3Aand 3B;

FIG. 5B is a potential diagram taken along the line a-a′ of FIG. 5A;

FIG. 6A is a cross-sectional diagram taken along the line III-III′ ofFIGS. 3A and 3B;

FIG. 6B is a potential diagram taken along the line b-b′ of FIG. 6A;

FIG. 7A is a cross-sectional view taken along the line IV-IV′ of FIGS.3A and 3B;

FIG. 7B is a potential diagram taken along the line c-c′ of FIG. 7A.

FIGS. 8A, 8B, 9A-9C and 10 are diagrams illustrating methods ofmanufacturing an image sensor according to some embodiments;

FIGS. 11 and 12 are diagrams illustrating optical masks that can be usedin methods of manufacturing an image sensor according to someembodiments; and

FIG. 13 is a schematic diagram illustrating a system based on aprocessor that includes an image sensor according to some embodiments.

DETAILED DESCRIPTION

Embodiments of the present invention now will be described more fullyhereinafter with reference to the accompanying drawings, in whichembodiments of the invention are shown. This invention may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein. Rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the invention to those skilled in the art.Like numbers refer to like elements throughout.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the present invention. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises,”“comprising,” “includes” and/or “including” when used herein, specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms used herein should be interpreted ashaving a meaning that is consistent with their meaning in the context ofthis specification and the relevant art and will not be interpreted inan idealized or overly formal sense unless expressly so defined herein.

It will be understood that when an element such as a layer, region orsubstrate is referred to as being “on” or extending “onto” anotherelement, it can be directly on or extend directly onto the other elementor intervening elements may also be present. In contrast, when anelement is referred to as being “directly on” or extending “directlyonto” another element, there are no intervening elements present. Itwill also be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present.

Relative terms such as “below” or “above” or “upper” or “lower” or“horizontal” or “lateral” or “vertical” may be used herein to describe arelationship of one element, layer or region to another element, layeror region as illustrated in the figures. It will be understood thatthese terms are intended to encompass different orientations of thedevice in addition to the orientation depicted in the figures.

Embodiments of the invention are described herein with reference tocross-section illustrations that are schematic illustrations ofidealized embodiments (and intermediate structures) of the invention.The thickness of layers and regions in the drawings may be exaggeratedfor clarity. Additionally, variations from the shapes of theillustrations as a result, for example, of manufacturing techniquesand/or tolerances, are to be expected. Thus, embodiments of theinvention should not be construed as limited to the particular shapes ofregions illustrated herein but are to include deviations in shapes thatresult, for example, from manufacturing. For example, an implantedregion illustrated as a rectangle will, typically, have rounded orcurved features and/or a gradient of implant concentration at its edgesrather than a discrete change from implanted to non-implanted regions.Likewise, a buried region formed by implantation may result in someimplantation in the region between the buried region and the surfacethrough which the implantation takes place. Thus, the regionsillustrated in the figures are schematic in nature and their shapes arenot intended to illustrate the actual shape of a region of a device andare not intended to limit the scope of the invention.

FIG. 1 is a block diagram illustrating an image sensor according to someembodiments.

Referring to FIG. 1, an image sensor according to some embodiments ofthe present invention includes an active pixel sensor array (APS array)10, a timing generator 20, a row decoder 30, a row driver 40, acorrelated double sampler (CDS) 50, an analog-to-digital converter (ADC)60, a latch 70, and a column decoder 80.

The active pixel sensor array 10 includes a plurality of unit pixelsthat are arranged two-dimensionally. The plurality of unit pixelsconvert an optical image into an electrical signal. The active pixelsensor array 10 receives a plurality of driving signals, such as a pixelselection signal ROW, a reset signal RST, and a charge-transfer signalTG, from the row driver 40, and is then driven. Further, the convertedelectrical signal is applied to the correlated double sampler 50 througha vertical signal line.

The timing generator 20 applies a timing signal and a control signal tothe row decoder 30 and the column decoder 80.

The row driver 40 applies a plurality of driving signals to drive aplurality of unit pixels according to the result decoded by the rowdecoder 30 to the active pixel sensor array 10. In general, when unitpixels are disposed in a matrix, a driving signal is applied for eachrow.

The correlated double sampler 50 receives an electric signal, which isgenerated in the active pixel sensor array 10, through a vertical signalline, and holds and samples the electric signal. The correlated doublesampler 60 performs double sampling on a specific reference voltagelevel (hereinafter, referred to as “noise level”) and a voltage level(hereinafter, referred to as “signal level”) of the generated electricsignal, and outputs a difference level between the noise level and thesignal level.

The analog-to-digital converter 60 converts an analog signalcorresponding to the difference level into a digital signal, and outputsthe digital signal.

The latch 70 latches the digital signal, and the latched signal issequentially output to an image-signal processor (not shown) accordingto the result decoded by the column decoder 80.

FIG. 2 is a circuit diagram illustrating a unit pixel of an image sensoraccording to some embodiments.

Referring to FIG. 2, a unit pixel 100 of the image sensor includes aphotoelectric-converting unit 110, a charge-detecting unit 120, acharge-transferring unit 130, a reset unit 140, an amplifying unit 150,and a selecting unit 160. In some embodiments, the unit pixel 100includes four transistors, as shown in FIG. 2. However, the unit pixel100 may include five transistors.

The photoelectric-converting unit 110 absorbs incident light andaccumulates charges that correspond to a quantity of light. Thephotoelectric-converting unit 110 may include a photodiode, aphototransistor, a photo gate, a pinned photodiode (PPD), and/or acombination thereof.

A floating diffusion region (FD) can be used as the charge-detectingunit 120. The charge-detecting unit 120 receives the charges that areaccumulated by the photoelectric-converting unit 110. Since thecharge-detecting unit 120 has parasitic capacitance, the charges areaccumulated in the charge-detecting unit 120. Further, since thecharge-detecting unit 120 is electrically connected to a gate of theamplifying unit 150, the charge-detecting unit 120 controls theamplifying unit 150.

The charge-transferring unit 130 transfers the charges from thephotoelectric-converting unit 110 to the charge-detecting unit 120. Ingeneral, the charge-transferring unit 130 includes one transistor, andis controlled by a charge-transfer signal TG.

The reset unit 140 periodically resets the charge-detecting unit 120. Asource of the reset unit 140 is connected to the charge-detecting unit120, and a drain thereof is connected to a voltage source VDD. Inaddition, the reset unit 140 is driven in response to a reset signalRST.

The amplifying unit 150 constitutes a source follower buffer amplifiertogether with a constant current source (not shown) that is locatedoutside the unit pixel 100. A voltage, which changes in response to avoltage of the charge-detecting unit 120, is output to the verticalsignal line 162. A source of the amplifying unit 150 is connected to adrain of the selecting unit 160, and a drain thereof is connected to thevoltage source VDD.

The selecting unit 160 selects the unit pixels 100 to be read in a rowunit. The selecting unit 160 is driven in response to a selection signalROW, and a source thereof is connected to a vertical signal line 162.

Further, driving signal lines 131, 141, and 161 of thecharge-transferring unit 130, the reset unit 140, and the selecting unit160 extend in a row direction (horizontal direction) such that unitpixels included in the same row are driven simultaneously.

FIG. 3A is a layout diagram illustrating color filters of an imagesensor according to some embodiments. FIG. 3B is a schematic plan viewillustrating an active pixel sensor array of an image sensor accordingto some embodiments. FIG. 4 is a cross-sectional view taken along theline I-I′ of FIGS. 3A and 3B. FIG. 5A is a cross-sectional view takenalong the line II-II′ of FIGS. 3A and 3B. FIG. 5B is a potential diagramtaken along the line a-a′ of FIG. 5A. FIG. 6A is a cross-sectionaldiagram taken along the line III-III′ of FIGS. 3A and 3B. FIG. 6B is apotential diagram taken along the line b-b′ of FIG. 6A. FIG. 7A is across-sectional view taken along the line IV-IV′ of FIGS. 3A and 3B.FIG. 7B is a potential diagram taken along the line c-c′ of FIG. 7A.

Referring to FIGS. 3A and 3B, in an image sensor according to someembodiments, a plurality of unit pixels are disposed in a matrix, and aplurality of color filters are disposed to correspond to the pluralityof unit pixels. In FIG. 3A, Bayer color filters are shown, but thepresent invention is not limited thereto. Unit pixels are disposed belowred color filters R, green color filters G, and blue color filters B tocorrespond thereto. In some embodiments, unit pixels that correspond tothe red color filters R, unit pixels that correspond to the green colorfilters G, and unit pixels that correspond to the blue color filters Bare defined as red unit pixels 100R, green unit pixels 100G, and blueunit pixels 100B, respectively.

FIG. 4 is a cross-sectional view taken along the line I-I′ of FIGS. 3Aand 3B, which is a cross-sectional view of a red unit pixel 100R, agreen unit pixel 100G, and a blue unit pixel 100B that are adjacent toeach other. FIG. 5A, FIG. 6A, and FIG. 7A are cross-sectional viewstaken along the lines II-II′, III-III′, and IV-IV′ of FIGS. 3A and 3B,which are cross-sectional views of a red unit pixel 100R, a green unitpixel 100G, and a blue unit pixel 100B.

In some embodiments, the image sensor includes a semiconductor substrate101, a deep well 107, an element-separation region 109, and a pluralityof unit pixels. It will be appreciated that the semiconductor substrate101 could include, for example, a semiconductor layer on a supportingsubstrate, such as a semiconductor substrate or an insulating substrate.The plurality of unit pixels include red unit pixels 100R, green unitpixels 100G, and blue unit pixels 100B. The red unit pixel 100R, thegreen unit pixel 100G, and the blue unit pixel 100B includephotoelectric-converting units 110R, 110G, and 110B, respectively. Eachof the red unit pixel 100R, the green unit pixel 100G, and the blue unitpixel 100B further includes the charge-detecting unit 120 and thecharge-transferring unit 130. In the present embodiment, pinnedphotodiodes (PPD) are used as the photoelectric-converting units 110R,110G, and 110B, but the present invention is not limited thereto.

The semiconductor substrate 101 has a first conductive type (forexample, N-type). The semiconductor substrate 101 is divided into lowerand upper substrate regions 101 a and 101 b by a second conductive (forexample, P-typed) deep well 107 that is formed at a predetermined depthof the semiconductor substrate 101. In the present embodiment, thesemiconductor substrate 101 is N-type, but the present invention is notlimited thereto.

The deep well 107 forms a potential barrier to prevent charges generatedin a deep region of the lower substrate region 101 a from flowingthrough the photoelectric-converting unit 110. The deep well 107increases recombination between electrons and holes. Accordingly, thedeep well 107 can decrease crosstalk between pixels due to random driftof the charges.

The deep well 107 may be formed such that it has the highestconcentration at the depth of 3 to 12 μm from the surface of thesemiconductor substrate 101, and has a layer thickness of 1 to 5 μm. Inthis case, the dimension that corresponds to the depth of 3 to 12 μm issubstantially the same as the dimension of the absorption wavelength ofred or near infrared region light in silicon. In this case, when thedepth of the deep well 107 from the surface of the semiconductorsubstrate 101 is shallow, a diffusion-prevention effect is excellent,and thus crosstalk is decreased. However, since the depth of a region ofthe photoelectric-converting unit 110 becomes shallow, it is possible tolower sensitivity with respect to incident light that has a longwavelength (for example, red light), whose photoelectric conversionratio is relatively large in deep regions. Accordingly, a location wherethe deep well 107 is formed may be adjusted according to a wavelengthregion of the incident light.

The element-separation region 109 is formed in the upper substrateregion 101 b and defines an activation region. In general, theelement-separation region 109 can include a FOX (Field OXide) formedusing an STI (Shallow Trench Isolation) or a LOCOS (Local Oxidation ofSilicon) method. A second conductive (for example, P-typed) separationwell (not shown) may be formed below the element-separation region 109.

Each of the photoelectric-converting units 100R, 100G, and 100B that areprovided in the red unit pixel 100R, the green unit pixel 100G, and theblue unit pixel 100B includes a P+-type pinning layer 112 and an N-typefirst photodiode 114, which are formed in the semiconductor substrate101.

The pinning layer 112 reduces a dark current by reducing electron-holepairs (EHP) that are thermally generated in the upper substrate region101 b. Charges that are generated to correspond to incident light ofeach wavelength are accumulated in the first photodiode 114. Further, amaximum impurity concentration of the photodiode 114 may be 1×10¹⁵ to1×10¹⁸ atom/cm³, and a maximum impurity concentration of the pinninglayer 112 may be 1×10¹⁷ to 1×10²⁰ atom/cm³. However, the presentinvention is not limited thereto, because the doped concentrations andlocations may be changed according to manufacturing process and/ordesign considerations.

The photoelectric-converting unit 110R of the red unit pixel 100Rincludes a second photodiode 116. That is, the photoelectric-convertingunit 110R of the red unit pixel 100R includes a pinning layer 112, afirst photodiode 114, and a second photodiode 116.

The second photodiode 116 is N-type, and is formed below the firstphotodiode 114. The second photodiode 116 is formed to have a lowerimpurity concentration than the first photodiode 114. The red light,which is incident on the photoelectric-converting unit 110R of the redunit pixel 100R, is incident on a deep region of the semiconductorsubstrate 101. Red light has a wavelength of approximately 650 to 700nm, and can penetrate to a deeper region of a semiconductor substratethan blue light or green light. The photoelectric-converting unit 110Rof the red unit pixel 100R includes not only the first photodiode 114but also the second photodiode 116, which is provided below the firstphotodiode 114. Therefore, the photoelectric-converting unit 110R canstore charges that are generated by a red wavelength, which can reach adeeper region of the substrate 101.

Light that reaches a deep region of the semiconductor substrate 101 mayspread more in a horizontal direction than light absorbed in the upperregion of the semiconductor substrate 101. For this reason, chargesgenerated by the light that has reached the deep region of thesemiconductor substrate 101, may more easily diffuse to neighboringregions of the substrate 101. The second photodiode 116 is formed tohave a relatively large width in a horizontal direction rather than avertical direction. Accordingly, charges generated by light that hasreached the deep region of the semiconductor substrate 101 can bemaximally stored, thereby reducing/preventing the charges from diffusingto the neighboring regions. In FIG. 4 and FIG. 5A, the second photodiode116 has a larger width W1 than the first photodiode 114, but the presentinvention is not limited thereto.

FIG. 5B is a potential diagram taken along the line a-a′ of FIG. 5A,which is a longitudinal potential diagram of a photoelectric-convertingunit 110R of a red unit pixel 100R. Referring to FIG. 5B, as comparedwith the slope of the potential (displayed by the dotted line) when onlythe first photodiode 114 is provided, the slope of the potential(displayed by the solid line) when the first photodiode 114 and thesecond photodiode 116 are provided is flatter. Accordingly, electrons ina deeper region can also be captured. In this case, since an impurityconcentration of the second photodiode 116 is lower than an impurityconcentration of the first photodiode 114, the inclination of thepotential is formed, as shown in FIG. 4B. The electrons that aregenerated in the deep region move upward due to the potentialdifference. Further, the electrons move to the charge-detecting unit viathe charge-transporting unit.

When the impurity concentration in the second photodiode 116 is similarto that of the first photodiode 114, the slope of the potential maybecome even flatter (for example, may become horizontal). In this case,since the potential difference in the upper and lower regions of thesemiconductor substrate 101 decreases, it may become difficult for theelectrons in the deep region to move the upper region. That is, in theimage sensor according to this embodiment, the second photodiode 116,which corresponds to an impurity region having a lower concentrationthan the first photodiode 114, is formed below the first photodiode 114of the red unit pixel 100R. As a result, the electrons that aregenerated in the deep region can be captured, and the electrons that arecaptured by the second photodiode 116 can more easily move to the upperregion of the semiconductor substrate 101 due to the potentialdifference in the upper and lower regions of the semiconductor substrate101.

The photoelectric-converting unit 110G of the green unit pixel 100Gincludes a third photodiode 118. That is, the photoelectric-convertingunit 110G of the green unit pixel 100G includes a pinning layer 112, afirst photodiode 114, and a third photodiode 118.

The third photodiode 118 is formed below the first photodiode 114, andhas N-type conductivity like the first photodiode 114. The thirdphotodiode 118 is formed to have a lower impurity concentration than thefirst photodiode 114. Further, the third photodiode 118 may be formed atsubstantially the same depth as the second photodiode 116. The greenwavelength, which is incident on the photoelectric-converting unit 110Gof the green unit pixel 100G, is incident on a deep region in thesemiconductor substrate 101. Green light has a wavelength ofapproximately 490 to 550 nm, and penetrates to a shallower depth thanred light, but deeper than blue light. The photoelectric-converting unit110G of the green unit pixel 100G includes not only the first photodiode114 but also the third photodiode 118, which is provided below the firstphotodiode 114. Therefore, the photoelectric-converting unit 110G canalso store charges that are generated by green light, which can reach adeeper region.

The third photodiode 118 is formed to have a smaller width than thefirst and second photodiodes 114 and 116. In this case, the width of thethird photodiode 118 means an area of the third photodiode 118 when thethird photodiode 118 is cut in a horizontal direction at the same level.Since FIGS. 4, 6A, and 7A are cross-sectional views, the width W1 of thesecond photodiode 116 and the width W2 of the third photodiode 118 areshown. It is more difficult for green light to penetrate to the deepregion of the semiconductor substrate 101, as compared with red light.Accordingly, the amount of charges generated in the deep region of thegreen unit pixel 100G, may be smaller than the amount of chargesgenerated in the deep region of the red unit pixel 100R. Thus, eventhough the width of the third photodiode 118, which is formed in thephotoelectric-converting unit 110G of the green unit pixel 100G, issmaller than the width of the second photodiode 116, which is formed inthe photoelectric-converting unit 110R of the red unit pixel 100R, it ispossible to sufficiently capture electrons that are generated in thedeep region of the green unit pixel 100G. Since the third photodiode 118is formed to have a smaller width than the first and second photodiodes114 and 116, the distance (W3 of FIG. 4) in a horizontal directionbetween the third photodiode 118 and the second photodiode 116, which isformed adjacent to the third photodiode 118, is increased.

In the deeper region of the semiconductor substrate 101, impurityregions can more easily diffuse, as compared with the upper region ofthe semiconductor substrate 101. Because of the diffusion of theimpurity regions, blooming occurs, thereby lowering the reliability ofthe image sensor. Accordingly, when the distance between the impurityregions and the deep region is increased, the reliability of the imagesensor can be improved. In the present embodiment, in the image sensor,the photoelectric-converting unit 110G of the green unit pixel 100Gincludes a third photodiode 118 that is formed below the firstphotodiode 114. Accordingly, the width of the third photodiode 118 canbe decreased while the electrons formed in the deep region are captured,and thus the diffusion of impurities and blooming can be reduced. As aresult, it is possible to improve the reliability of the image sensor.

FIG. 6B is a potential diagram taken along the line VIB-VIB of FIG. 6A,which is a longitudinal potential diagram of a photoelectric-convertingunit 110G of a green unit pixel 100G. Referring to FIG. 6B, as comparedwith an inclination of the potential (displayed by a dotted line) ofwhen the first photodiode 114 is only provided, a slope of the potential(displayed by a solid line) of when the first photodiode 114 and thesecond photodiode 116 are provided is flatter. Accordingly, it can beconfirmed that electrons in a deeper region can also be captured. Whenthe third photodiode 118 is formed at substantially the same depth asthe second photodiode 116, the potential diagram of thephotoelectric-converting unit 110G of the green unit pixel 100G may besimilar to the potential diagram of the photoelectric-converting unit110R of the red unit pixel 100R, as shown in FIGS. 5B and 6B. However,the present invention is not limited thereto.

The photoelectric-converting unit 110B of the blue unit pixel 100Bincludes a pinning layer 112 and a first photodiode 114. In thephotoelectric-converting unit 110B of the blue unit pixel 100B, the sameconductive impurity region as the first photodiode 114 is not providedbelow the first photodiode 114.

Blue light has a wavelength of approximately 430 to 480 nm. Since theblue wavelength is short, the blue wavelength may penetrate less deeplyinto the semiconductor substrate 101. Approximately 80% or more of bluelight may be absorbed in the surface of the semiconductor substrate 101at the depth of approximately 0.5 μm or less, and almost all the bluewavelength may be absorbed at the depth of approximately 2 μm or less.If the depth of the first photodiode 114 is in a range of approximately1 to 5 μm, almost all the blue wavelength is absorbed in the firstphotodiode 114. Accordingly, a separate impurity region may not need tobe formed below the first photodiode 114.

FIG. 7B is a potential diagram taken along the line c-c′ of FIG. 7A,which is a longitudinal potential diagram of a photoelectric-convertingunit 110B of a blue unit pixel 100B. Referring to FIG. 7B, it can beunderstood that a slope of the potential (displayed by a solid line) ofthe photoelectric-converting unit 110B of the blue unit pixel 100B,where only the first photodiode 114 is provided, is large, as comparedwith those shown in FIGS. 5B and 6B. That is, charges that are generatedin the deep region of the semiconductor substrate 101 may not becaptured in the photoelectric-converting unit 110B of the blue unitpixel 100B. Accordingly, even when there are electrons that have movedfrom the adjacent red unit pixel 100R or the adjacent green unit pixel100G, the electrons may not be captured by the photoelectric-convertingunit 110B of the blue unit pixel 100B.

That is, in some embodiments, in the green unit pixel 100G of the imagesensor, the first photodiode 114 may capture electrons that aregenerated from blue light, but may not capture electrons that have movedfrom an adjacent unit pixel. As a result, it is possible to improvecolor reproducibility.

Referring to FIGS. 5A, 6A and 7A, the charge-detecting unit 120 isformed in the semiconductor substrate 101, and receives the chargesaccumulated in the photoelectric-converting units 110R, 110G, and 110Bthrough the charge-transferring unit 130. The charge-transferring unit130 includes an impurity region 132, a gate insulating layer 134, a gateelectrode 136, and a spacer 138.

The impurity region 132 can reduce a dark current that can be generatedregardless of an image that is sensed in a state where thecharge-transferring unit 130 is turned off. The impurity region 132 isformed adjacent to the surface of the upper substrate region 101 b, andreduces the dark current. The impurity region 132 may be formed at adepth of, for example, 2000 Å or less.

The gate insulating layer 134 may be made of SiO₂, SiON, SiN, Al₂O₃,Si₃N₄, Ge_(x)O_(y)N_(z), Ge_(x)Si_(y)O_(z), and/or high dielectricmaterials. In this case, the high dielectric materials may be formed byan atomic layer deposition method using HfO₂, ZrO₂, Al₂O₃, Ta₂O₅,hafnium silicate, zirconium silicate, and/or a combination thereof.Further, the gate insulating layer 134 may be configured by laminatingtwo or more materials selected from the materials of the exemplifiedlayers as a plurality of layers. The gate insulating layer 134 may beformed to have a thickness in the range of 5 to 100 Å.

The gate electrode 136 may include a metal film, such as a conductivepolysilicon film, W, Pt, or Al, a metal nitride film, such as TiN, ametal silicide film that is obtained from a refractory metal, such asCo, Ni, Ti, Hf, and Pt, and/or a combination thereof. Alternatively, thegate electrode 136 may be formed by sequentially laminating a conductivepolysilicon film and a metal silicide film, or a conductive polysiliconfilm and a metal film. However, the present invention is not limitedthereto.

The spacer 138 is formed at both sidewalls of the gate electrode 136,and may include a nitride film (SiN).

FIGS. 8A to 10 are diagrams illustrating methods of manufacturing animage sensor according to some embodiments. Methods of manufacturing animage sensor according to some embodiments will be described withreference to FIGS. 3B, 4A, 4B, and 8A to 10.

First, referring to FIGS. 8A and 8B, impurities are implanted into apredetermined region of the semiconductor substrate 101 of the firstconductive type to form the deep well 107. The element-separation region109 is formed to define an active region 102 where pixels and peripheralcircuits are to be formed.

At this time, regions where red unit pixels, green unit pixels, and blueunit pixels are formed are defined in the semiconductor substrate 101.In FIG. 8B, reference character R denotes a red unit pixel region,reference character G denotes a green unit pixel region, and referencecharacter B denotes a blue unit pixel region.

When an N-type substrate is used, the deep well 107 may be formed byimplanting a second conductive ion, different from the conductivity ofthe semiconductor substrate 101. Further, impurities may be implantedbelow the element-separation region 109, thereby forming a separationwell (not shown) to reduce crosstalk in a horizontal direction.

Then, referring to FIGS. 9A to 9C, a mask pattern 250, where firstopenings 252 are formed in the red unit pixel regions and secondopenings 254 are formed in the green unit pixel regions, is formed onthe semiconductor substrate 101.

FIG. 9A shows an optical mask 200 that may be used to form the maskpattern 250. The optical mask 200 includes first light-transmittingportions 210 that are formed in regions 200R corresponding to the redunit pixel regions and second light-transmitting portions 220 that areformed in regions 200G corresponding to the green unit pixel regions.The first light-transmitting portion 210 may be formed to have a largerarea than the second light-transmitting portion 220, andlight-transmitting portions may not be formed in regions 200Bcorresponding to the blue unit pixel regions.

Specifically, a mask layer, for example, a photoresist layer is formedon the semiconductor substrate 101, and then a photolithography processis performed by using the optical mask 200 shown in FIG. 9A, therebyforming the mask pattern 250. As a result, in the mask pattern 250, thefirst openings 252 are formed in the regions that correspond to thefirst light-transmitting portions 210, and the second openings 254 areformed in the regions that correspond to the second light-transmittingportions 220. That is, the first opening 252 is formed in the red unitpixel region 200R, and the second opening 254 is formed in the greenunit pixel region 200G. At this time, the first opening 252 is formed tohave a larger area than the second opening 254.

Referring to FIGS. 9B and 9C, before forming the mask pattern 250,transistors including charge-transferring units and a pinning layer 112are formed. However, the present invention is not limited thereto. Afterforming the mask pattern 250, the transistors including thecharge-transferring units and the pinning layer 112 may be formed.

Then, referring to FIG. 10, the mask pattern (refer to reference numeral250 of FIG. 9C) is used as an ion implantation mask and an ionimplantation process is performed, thereby forming the second photodiode116 and the third photodiode 118.

At this time, since the area of the first opening (refer to referencenumeral 252 of FIG. 9C) is larger than the area of the second opening(refer to reference numeral 254 of FIG. 9C), the second photodiode 116is formed to have a larger width than the third photodiode 118. Further,since the second photodiode 116 and the third photodiode 118 are formedby the same ion implantation process, ion implantation energy and a doseof implanted ions are the same. Accordingly, the second photodiode 116and the third photodiode 118 can be formed with the same concentrationat substantially the same depth.

Then, referring to FIGS. 3B and 4A and 4B, the first photodiodes 114 areformed in the red unit pixel regions, the green unit pixel regions, andthe blue unit pixel regions.

The first photodiode 114 is formed on the second and third photodiodes116 and 118, and may be formed to be substantially the same type in thered, green, and blue unit pixel regions.

Then, the red unit pixel 100R, the green unit pixel 100G, and the blueunit pixel 100B are finished using processes known to those skilled inthe art.

In some embodiments, the first photodiode 114 is formed after formingthe second and third photodiodes 116 and 118 that are located in thedeeper region, but the present invention is not limited thereto. Thatis, the second and third photodiodes 116 and 118 may be formed afterforming the first photodiode 114.

According to some embodiments, the regions of the second and thirdphotodiodes 116 and 118 are formed in the photoelectric-converting unit110R of the red unit pixel 100R and the photoelectric-converting unit110G of the green unit pixel 100G, respectively, to capture electronsthat are generated by a wavelength absorbed in the deep region of thesemiconductor substrate 101, thereby improving color reproducibility.Since the width of the second photodiode 116 of the red unit pixel 100Rwhere the light reaching the deep region has a large wavelength islarger than the width of the third photodiode 118, it is possible toefficiently capture electrons. Further, since the width of the thirdphotodiode 118 is smaller than the width of the second photodiode 116,the spacing between the second photodiode 116 and the third photodiode118 can be relatively increased. Further, in the region of the blue unitpixel 100B where the electrons in the deep region do not need to becaptured, the impurity region may not be formed. Accordingly, it ispossible to efficiently capture electrons in the deep region whilereducing/preventing the “blooming” phenomenon that can occur whenimpurity regions that are formed in the deep region of the semiconductorsubstrate 101 diffuse toward each other. Therefore, it is possible toimprove the reliability of the image sensor.

According to some embodiments, the second and third photodiodes 116 and118 are formed by performing a photolithography process using a singleoptical mask one time. That is, impurity regions whose widths aredifferent from each other are formed by performing a photolithographyprocess once, thereby improving productivity.

FIGS. 11 and 12 are diagrams illustrating optical masks that can be usedin methods of manufacturing an image sensor according to someembodiments.

The optical mask 202 shown in FIG. 11 is different from the optical mask200 shown in FIG. 9A in that each of first and second light-transmittingportions 212 and 222 is formed in a rectangular shape. However, thefirst and second openings 212 and 222 are not limited thereto, and mayhave all polygonal types. That is, the first and second openings 212 and222 include all types in which the area of the first light-transmittingportion 212 is larger than the area of the second light-transmittingportion 222. In this case, reference numeral 202R denotes a region thatcorresponds to the red unit pixel region, reference numeral 202G denotesa region that corresponds to the green unit pixel region, and referencenumeral 202B denotes a region that corresponds to the blue unit pixelregion.

The optical mask 204 shown in FIG. 12 is different from the optical mask200 shown in FIG. 9A in that the first light-transmitting portion 214 isformed in a square shape and the second light-transmitting portion 224is formed in a rectangular shape.

The second light-transmitting portion 224, which is formed in the region204G corresponding to the green unit pixel region shown in FIG. 12, isseparated from the first light-transmitting portion 214 that is formedin the region 204R that corresponds to the red unit pixel region. As aresult, it is possible to increase an interval between the secondphotodiode, which is to be formed to correspond to the firstlight-transmitting portion 214, and the third photodiode, which is to beformed to correspond to the second light-transmitting portion 224.Meanwhile, the second light-transmitting portion 224 is formed to extendalong the region 204B that corresponds to the blue unit pixel regionwhere impurity regions do not exist at the same level. That is, thesecond light-transmitting portion 224 extends along the region 204B thatcorresponds to the blue unit pixel region where the impurity regions donot exist at the same level, and it is not likely for the impurityregions to diffuse to the adjacent impurity regions. Therefore, it ispossible to further capture the electrons that are generated in the deepregion.

FIG. 13 is a schematic diagram illustrating a system based on aprocessor that includes an image sensor according to embodiments of thepresent invention.

Referring to FIG. 13, a processor-based system 300 processes an outputimage of a CMOS image sensor 310. Examples of the processor-based system300 may include a computer system, a camera system, a scanner, amechanized clock system, a navigation system, a video phone, asupervising system, an auto-focusing system, a tracking system, anoperation-monitoring system, and an image-stabilizing system. However,the present invention is not limited thereto.

The processor-based system 300, such as the computer system, includes acentral processing unit (CPU) 320, such as a microprocessor, which iscapable of communicating with an input/output (IO) element 330 through abus 305. The CMOS image sensor 310 can communicate with a system throughthe bus 305 or another communication link. The processor-based system300 may further include a RAM 340 that can communicate with the CPU 320through the bus 305, a floppy disk drive 350 and/or a CD ROM drive 355,and a port 360. The port 360 can couple a video card, a sound card, amemory card, and a USB element, or exchange data with another system.The CMOS image sensor 310 can be integrated together with a CPU, adigital signal processing device DSP or a microprocessor. The CMOS imagesensor 310 can be integrated together with a memory. In some cases, theCMOS image sensor 310 can be integrated in a chip different from theprocessor.

According to some embodiments, an image sensor includes a red unit pixelincluding first and second photodiodes, and a green unit pixel includingfirst and third photodiodes. The second and third photodiodes are formedin the photoelectric-converting units of the red unit pixel and thegreen unit pixel, respectively, to capture the electrons that aregenerated by the wavelength absorbed in a deep region of thesemiconductor substrate, thereby improving color reproducibility. Thewidth of the second photodiode of the red unit pixel where the lightreaching the deep region has a long wavelength is larger than the widthof the third photodiode. As a result, the spacing between the secondphotodiode and the third photodiode is relatively large and the impurityregions may not need to be separately formed in the blue unit pixelregion. Accordingly, electrons in the deep region can be efficientlycaptured while it is possible to reduce or prevent the bloomingphenomenon that can occur when impurity regions that are formed in thedeep region of the semiconductor substrate diffuse, thereby improvingthe reliability of the image sensor.

Further, the second and third photodiodes can be formed by performing aphotolithography process using a single optical mask one time. That is,impurity regions whose widths are different from each other can beformed by performing a photolithography process once, thereby improvingproductivity.

In the drawings and specification, there have been disclosed typicalembodiments of the invention and, although specific terms are employed,they are used in a generic and descriptive sense only and not forpurposes of limitation, the scope of the invention being set forth inthe following claims.

1. An image sensor comprising: a semiconductor layer; and first and second photoelectric converting units comprising first and second impurity regions respectively in the semiconductor layer that are spaced apart from each other and that are at about an equal depth in the semiconductor layer, each of the impurity regions comprising an upper region and a lower region, wherein a width of the lower region of the first impurity region is larger than a width of the lower region of the second impurity region, and widths of upper regions of the first and second impurity regions are about equal.
 2. The image sensor of claim 1, further comprising: a third photoelectric converting unit comprising a third impurity region in the semiconductor layer that is spaced apart from the first and second impurity regions in the semiconductor layer, wherein a width of the third impurity region is about equal to the widths of the upper regions of the first and second impurity regions, and a depth of the third impurity region is shallower than depths of the first and second impurity regions.
 3. The image sensor of claim 2, wherein: the first impurity region is configured to accumulate charges corresponding to incident light having a wavelength in the red region, the second impurity region is configured to accumulate charges corresponding to incident light having a wavelength in the green region, and the third impurity region is configured to accumulate charges corresponding to incident light having a wavelength in the blue region.
 4. The image sensor of claim 1, wherein an impurity concentration of the upper region of the first impurity region is higher than an impurity concentration of the lower region of the first impurity region.
 5. The image sensor of claim 1, wherein an impurity concentration of the upper region of the second impurity region is higher than an impurity concentration of the lower region of the second impurity region.
 6. The image sensor of claim 1, wherein an impurity concentration is about equal in the lower regions of the first and second impurity regions.
 7. The image sensor of claim 1, wherein a spacing between the upper regions of the first and second impurity regions is smaller than a spacing between the lower regions of the first and second impurity regions.
 8. The image sensor of claim 1, wherein a width of the lower region of the second impurity region is smaller than a width of the upper region of the second impurity region.
 9. The image sensor of claim 1, wherein the first impurity region and the second impurity region are impurity regions of the same conductivity type.
 10. The image sensor of claim 1, wherein the semiconductor layer comprises a semiconductor substrate. 